Polymeric material reinforced with metal elements such as steel wires or steel cords are widely applied in a variety of products such as conveyor belts, hoses and tires.
One of the critical problems to be solved is to achieve good adhesion between the metal element and the polymeric material.
Especially, for specialty rubbers such as chloroprene rubber, ethylene propylene diene monomer (EPDM) rubber, nitrile rubber as for example butadiene acrylonitrile (NBR) or hydrogenated butadiene acrylonitrile (HNBR), the adhesion between the metal element and the rubber remains critical.
The use of bifunctional silanes is known in the art to promote the adhesion of a metal element to a material to be reinforced. However, for many applications these bifunctional silanes do not provide an adequate adhesion between the metal element and the material to be reinforced.
Other coatings such as phenol-formaldehyde resins, halogenated polymers and olefin based polymer systems have been developed to promote the adhesion between a metal element and specialty rubbers.
A drawback of these coatings is that relative thick layers (usually between 25 and 50 μm) are necessary. Another drawback is that toxic solvents like xylene or perchloroethylene are used to apply these coatings on the metal elements.
Furthermore for many applications these coatings do not allow to reach the required adhesion level.